Toyota’s new magnet won’t depend on some key rare-earth minerals

Permanent magnet motors are here to stay, but we can make them less costly.

Further Reading

Toyota in “production engineering” for a solid state battery, WSJ says

Rare-earth magnets are used in many hybrid vehicles, some all-electric vehicles, and in other applications like wind turbines and robotics.

Although “rare” is a bit of a misnomer for a material like neodymium (high demand has led to relatively high production volumes), Toyota notes that “there are concerns that shortages will develop as electrified vehicles, including hybrid and battery electric vehicles, become increasingly popular in the future.” That concern is compounded by the concentration of rare-earth mining: although attempts have been made to mine rare-earth metals in the US and other parts of the world, a preponderance of rare-earth mining occurs in China. That country threatened to stop exporting neodymium and other rare earths in 2011, which sent prices for the metals soaring. If China were to use rare-earth access as a geopolitical tool again, it could significantly impact companies like Toyota that depend on rare earths to build flagship products like the Prius.

The new magnet Toyota developed also uses no terbium or dysprosium, which can be added to neodymium to improve its operability at high heat, above 100 degrees Celsius (212 degrees Fahrenheit). (In fact, mining consultancy Roskill notes that few automakers use terbium in magnets anymore, though dysprosium is still commonly added to magnets with neodymium.)

NdFeB magnets are able to produce a strong magnetic field in small volumes. When paired with dysprosium, NdFeB magnets have high coercivity, that is, “the ability to resist demagnetization once magnetized,” according to a 2015 paper from Sustainable Materials and Technologies.

In a Permanent Magnet (PM) AC car motor, NdFeB magnets are often embedded in the rotor. When wire windings in the stator are electrified, the magnetic attraction causes the rotor to rotate. In other designs, the magnets can be embedded in the stator, or the magnets can be arranged to work with a DC magnetic field. By contrast, induction motors (which are much more common) use no magnets and rely on current flowing through the stator windings to induce a magnetic field, which leads to the rotation of the rotor.

As you might imagine, there are several trade-offs between PM motors and magnet-less induction motors. Roskill notes PM-based systems tend to be lighter and smaller, since they can rely on the NdFeB magnet inside of them for a constant magnetic field. Most hybrid vehicles (HEVs) use PM systems: with a hybrid system you need both a battery and an internal combustion engine, so reducing the size of the motor is paramount. (Components-maker Bosch has also worked on building systems that use both induction motors and permanent magnet motors in the same product, for front and rear axles, for example.)

Tesla famously eschewed magnets in its Model S and Model X vehicles, opting for a heavier copper induction system. But the Model 3 reportedly does use a PM system, likely because magnets economize space and weight (which can affect battery range), and such motors tend to have better acceleration. The Chevy Bolt also uses a neodymium-based magnet, Roskill says.

Instead of neodymium or dysprosium, the magnet uses less-expensive rare-earth metals lanthanum and cerium. Certainly, this doesn’t get rid of many of the issues with neodymium: lanthanum and cerium are still predominantly mined in China and, as with most rare earths, they can be environmentally destructive to produce. But Reuters notes that while neodymium costs about $100 per kg and dysprosium costs about $400 per kg, lanthanum and cerium cost about $5 to $7 per kg. Ideally, a cheaper magnet could result in cheaper hybrid and all-electric vehicles.

Toyota used a few tricks to reduce its neodymium use. The company says that simply replacing the neodymium in a magnet with lanthanum and cerium results in a sub-par magnet with reduced coercivity and reduced heat resistance, meaning motor performance will suffer. Instead, the company composed the magnet so that most of the lanthanum and cerium grains were internal to the magnet, and most of the neodymium grains were on the outside.

The automaker also reduced the grain size of the metals in the magnet. This has been an avenue of research for some time: the 2015 Sustainable Materials and Technologies paper noted that finding a way to reliably reduce the grain size of components of rare earth magnets could increase the magnetic energy stored in a magnet. Toyota was apparently also pursuing that path. Its researchers were able to reduce the grain size of its magnets’ components to one-tenth of what is used in standard magnets.

These manufacturing techniques allow Toyota to lose 20 to 50 percent of the neodymium necessary to make a NdFeB magnet without losing performance or coercivity. Reuters notes that electric vehicle magnets will likely only be able to take advantage of the low end of that—but eliminating 20 percent of the neodymium you need in a vehicle magnet is good, too.

For now, the design is preliminary, and Toyota says it needs to conduct more research before adding these advanced magnets into its cars. By the early 2020s, the company hopes to use the magnets in power-steering systems, and then it hopes to move to wider use in electric vehicle motors within the decade.

Toyota has been a pioneer in the hybrid vehicle market, but it has been more hesitant in pushing all-electric vehicles to market. By all accounts, though, its researchers have been looking for ways to make electric vehicles cutting-edge. The company announced in summer 2017 that it was in “production engineering” for a solid-state battery, which would theoretically be lighter, smaller, and have a better range of operating temperatures than the batteries we see today on Teslas, Nissans, and Chevys.